1. Field of the Invention
The present invention relates to an articulated robot having a plurality of arms connected by angularly movable joints, and more particularly to an articulated robot movable in a wide horizontal range.
2. Description of the Related Art
It is often customary in vehicle manufacturing factories for workpieces to be progressively machined while being conveyed between a plurality of stations or machining units. The workpieces should desirably be conveyed quickly for increased productivity.
Proposed means for conveying workpieces include a reciprocatingly movable carriage for conveying workpieces between machining units, and a loader and an unloader for transferring workpieces between the carriage and the machining units (see, for example, Japanese Patent Publication No. 04-009611). The proposed means are capable of moving workpieces over a long distance.
Processes for conveying workpieces with articulated robots have also been proposed in the art (see, for example, Japanese Patent No. 2785597, Japanese Laid-Open Patent Publication No. 2006-123009, Japanese Patent No. 2726977, and Japanese Laid-Open Patent Publication No. 07-308876). The proposed processes for conveying workpieces with articulated robots are relatively simple because workpieces can be unloaded, conveyed, and loaded by a single articulated robot.
Using a carriage, a loader, and an unloader to convey a workpiece, as disclosed Japanese Patent Publication No. 04-009611, fails to convey the workpiece quickly because it is necessary to transfer the workpiece from the loader to the carriage and also from the carriage to the unloader. As it is also necessary to synchronize the workpiece transfer cycles, the overall control process is complex to perform. Furthermore, the carriage moves along paths provided by conveying frames which are fixedly installed depending on the distances between the machining units. Therefore, the conveying frames that have been fixedly installed once will not be applicable in the case where the layout of the machining units is to be changed.
In addition, since the three apparatus, i.e., the carriage, the loader, and the unloader, are required, they need a large installation space, and the cost of installing them is high.
The articulated robot disclosed in Japanese Patent No. 2785597 lacks a horizontally moving mechanism. When the articulated robot conveys the workpiece horizontally, the arm takes an elbow-up attitude and thus needs a wide vertical space for its movement.
The articulated robots disclosed in Japanese Laid-Open Patent Publication No. 2006-123009, Japanese Patent No. 2726977, and Japanese Laid-Open Patent Publication No. 07-308876 have horizontally angularly movable joints. However, since the disclosed articulated robots also have vertically angularly movable joints, the workpiece carried thereby and the arm move unnecessarily vertically, as with the articulated robot disclosed in Japanese Patent No. 2785597.
If the distances to convey workpieces between the machining units are long, then the arm of the articulated robot needs to be considerably long. However, the long arm tends to flex unduly due to its own weight and the weight of the workpiece carried thereby, resulting in a reduction in the accuracy with which the arm conveys the workpiece.